The present invention relates to a digital filter for a voice synthesis circuit which is derived on the basis of the principle of linear predictive coding; in particular, the present invention relates to a method of forming a digital filter for voice synthesis which is derived on the basis of the principle of linear predictive coding of the lattice type.
A digital filter of the lattice type was already described in detailed in chapter 5 of the book entitled "Linear Prediction of Speech", written by Markel and Gray (Springer-Verlag, New York, 1976).
The historical analysis of the means for fabricating said digital filter of the lattice type was disclosed in detail in Japanese Patent Laid-Open Specification No. 7838/1979 in which a means for fabricating a digital filter of the lattice type by using one multiplication circuit and one addition-subtraction circuit was proposed.